The River Walk is 15-miles long. It flows through approximately 5-miles of downtown San Antonio. As such, there is no one address. For GPS purposes, use the address for the Shops at Rivercenter, located directly on the River Walk, in the heart of downtown, at 849 E. Commerce Street, San Antonio, Texas 78205.
The headwaters of the San Antonio River is located at the University of Incarnate Word College in San Antonio, Texas. approximately 4 miles north of Downtown. It joins the Guadalupe River and flows all the way to the Gulf of Mexico.
See an overview map of River Walk at https://www.thesanantonioriverwalk.com/map